How to keep kids out of my yard???!!!!!?

That sounds horrible! I would say put a pad lock on the back fence or at least a latch that kids can't reach. I think it's more of a safety thing cause of the pool. What happens if one of these rude little kids hurt themselves on your property - guess who's parents are going to come calling about medical bills? I would also designate a play time where your kids can have their "friends" over to play and only let kids in during that time. You can explain that you're having family time if they ask why they can't play during times that you would like some peace and quiet. Their parents couldn't possible think you're "rocking the boat" cause you turned their kids away from your property to spend quality time with your family. If kids came into my property unannounced I would "ground" them - tell them they cannot play today cause they were rude by not knocking, removing shoes, coming in the back yard unannounced, etc. I don't care who's kid is in my house, if they don't behave at least as well as my child (after a few warnings) then they need to go home.